The official argument is that he needs to focus on immediate matters at hand, but this is clearly a warning as well as a preparation for his eventual removal:

Boeing Co.’s board stripped Chief Executive Dennis Muilenburg of his dual role as chairman on Friday in an unexpected shake-up at the highest ranks of the company amid the prolonged crisis of its 737 MAX plane.

Boeing said it took the action to allow Mr. Muilenburg to focus on running the company as it returns the MAX fleet to service after it was grounded world-wide in March following two fatal crashes in less than five months.

The leadership change came hours after a panel or air-safety experts sharply criticized Boeing and the U.S. Federal Aviation Administration for missteps that led to the crashes, which killed all 346 people on flights in Indonesia and Ethiopia. The report has added to criticism in Washington, D.C., where lawmakers are considering potential changes to aviation oversight.

David Calhoun, a senior Blackstone Group Inc. executive who has been the board’s lead director, will become its chairman. The board has “full confidence in Dennis as CEO and believes this division of labor will enable maximum focus on running the business with the board playing an active oversight role,” Mr. Calhoun said in a statement.

This is clearly a warning shot across Muilenbugg’s bow, and it’s also setting him up as a skapegoat for the 737 MAX debacle.

I expect him to be out before New Years Day, 2021.